1. Field of the Invention
The invention disclosed herein relates to sampling formation fluids and, more particularly to clean up of the samples.
2. Description of the Related Art
In the quest for hydrocarbons, boreholes are drilled into geologic formations that may contain reservoirs of the hydrocarbons. Drilling time can be very expensive due to personnel and drilling rig costs. In order to efficiently use drilling resources, samples of formation fluids are obtained from the formations using formation testers disposed in the boreholes. Based on sample tests such as chemical characterization, drilling decisions can be made to efficiently use the drilling resources.
A drilling fluid or mud is typically pumped through a drill string to a drill bit drilling a borehole in order to lubricate the drill bit and flush cuttings from the borehole. The drilling mud is present in the borehole and can enter pores of rock in the borehole wall where the drilling mud is called filtrate. A formation tester is used to extract a sample of formation fluid through the borehole wall. Unfortunately, filtrate can contaminate the sample. In order to minimize contamination, the formation fluid is continuously extracted over a time interval. During the time interval, when the amount of filtrate contamination decreases to an acceptable amount or to near zero and, then, a sample of the formation fluid is taken.
Depending on factors such as the type of rock and filtrate, it may take hours or even days to achieve levels of filtrate that are acceptable for characterization. It would be well received in the drilling industry if the formation testing art could be improved to decrease the amount of time required to obtain a sample of a formation fluid with an acceptable level of mud-filtrate contamination.